1. Field of the Invention
The present invention relates to a full-circumferential flow pump, and more particularly to a full-circumferential flow pump having an impeller on an end of a shaft of a motor, with an annular space or flow passage defined around the motor.
2. Description of the Prior Art
German laid-open patent publication No. 1,653,692 (DE 1,653,692) discloses a pump in which a fluid being handled flows around a motor. The disclosed pump allows its main shaft to be rotated manually and also allows pump units to be inspected and serviced for maintenance without the need for removing pipes connected to the pump.
FIG. 9 of the accompanying drawings shows the disclosed pump. As shown in FIG. 9, the pump has a block-like main body 100, a motor stator 101 housed therein, and a motor rotor 102 disposed in the motor stator 101 with a small clearance between the motor stator 101 and the motor rotor 102. Impellers 103, 104 are fixedly mounted on respective opposite ends of the motor rotor 102. A fluid flows from a pump suction port 105 into the block body 101, is divided into two lateral flows which are then pressurized by the impellers 103, 104. The impellers 103, 104 discharge the respective fluid flows, which are then merged and discharged from the main body 101 through a discharge port 106.
The disclosed pump shown in FIG. 4 is highly likely to suffer problems which arise due to pressure irregularities applied to the motor stator 101. More specifically, the pump has three different regions around the motor which include:
1) a region in which the fluid under a suction pressure flows;
2) a region in which the fluid under a discharge pressure flows; and
3) a region in which no fluid flows at all.
On account of these different regions, the pressure (external force) imposed on the motor stator 101 is not uniform, tending to strain or deform the motor stator 101.
Furthermore, since the discharge pressure is applied to the motor, especially its rotor chambers, the pump is not suitable for use in applications under high discharge pressure. The pump may possibly be open to difficulties when it is incorporated in a unit pump system in which pumps are series-connected to produce a high pump head.
The pump is highly liable to suffer drawbacks when an outer motor frame is made of thin sheet metal and also the pump discharge pressure is high. When subjected to external forces such as loads from the piping, the motor of the disclosed pump tends to cause trouble because the outer motor frame and an outer cylinder of the pump are integrally formed with each other.